Data storage is accomplished through various means in our society. Printed texts have been in existence for some time but suffer from fading and deterioration because of the underlying material on which the print is applied. In a similar manner, electronic data storage is also finite because the technologies utilized are usually reversible to allow read-write capabilities. For example, magnetic tapes are believed to have a lifespan of 10 to 30 years. Compact disc (“CD”) technology also suffers from material degradation as it utilizes a dye to store the data and this dye is prone to degradation. Estimates of the lifespan of CDs are typically between two to five years, depending on the quality of the CD. In contrast, vinyl records are known to have longer lifespans, in the order of 100 years. This increased performance is a direct result of data being physically grooved into the material to form ridges and the integrity of these ridges with time based on the slow deformation (flow) of vinyl with time. These ridges when turned against a needle cause vibrations to be converted into electrical signals and later sound. Unfortunately, however, the density of data that can be stored on such devices is limited because of the physical size of the grooves. A 12 inch vinyl record holds up to 45 minutes of music which corresponds to approximately 40 MB of memory. The memory density (or actually memory area) of this format is therefore in the order of 4 Mbits/in2. Table 1 summarizes this calculation.
TABLE 1Calculation of Memory Density for 12″ LPArea of Record113.1in2Area Non-Playable28.3in2Area Playable84.8in2Data Stored40Mbytes320 MbitsMemory Density3772562Bits/in23.77Mbits/in2
In contrast, the compact disc has a memory density in the order of 900 Mbits/in2, but does not have the memory longevity of the vinyl LP record. While hard drives have substantially higher memory densities, in the order of 150 Gbits/in2, these magnetic media similarly have limited longevities in the order of 5 to 30 years.
Conventionally, photolithography and e-beam lithography have been used to fabricate periodic ordered structures having nano- to micrometer feature sizes. Although these techniques are versatile in terms of complicated structures, these methods are limited by their high capital costs, selectivity of material types and inability to pattern curved and nonplanar surfaces.
A method of recording digital data in high density that retains data for a long period of time (>100 years) would therefore be highly desirable.